1. Field of the Invention
This invention relates to a polymerization initiator composition which controls polymerization at interface and a curable composition which contains it.
2. Description of the Prior Art
In the dental treatment, adhesion is required between dentins and polymeric, metallic, and other materials. Various adhesives have been proposed for the purpose of this adhesion. The idea underlying these adhesives comprises making effective use of a polymerizable monomer exhibiting affinity for dentins. Compounds possessing a carboxyl group include 4-methacryloyloxyethoxy carbonyl phthalic acid and anhydride thereof and 10-methacryloyloxy decyl malonic acid and compounds possessing a phosphoric acid group include 10-methacryloyloxy decyl dihydrodiene phosphate, for example. The polymerizable monomers which are mixable with such compounds include methyl methacrylate, bis-phenol A-glycidyl methacrylate adduct, and triethylene glycol dimethacrylate, for example.
As respects polymerization initiators for curing these polymerizable monomers, those which effect the curing by virtue of a free radical generated in a chemical reaction performed at room temperature (at about 25 .degree. C.) include benzoyl peroxide/amine type compounds, compounds of the same type additionally incorporating sulfinates therein, and tributyl boranes and oxides and those which attain the curing by dint of a free radical generated in a photoreaction include camphor-quinone/N,N-dimethylaminoethyl methacrylate and other type of amines, for example.
The conventional technique has placed emphasis on adhesive monomers. Even when a monomer capable of promoting adhesion is present on the interface of a dentin, no strong adhesive (bonding) strength is obtained unless the curing of this monomer proceeds inwardly from the interface thereof. Unless the polymerization initiator to be used is specially devised, it is only natural that owing to the shrinkage which occurs in consequence of the polymerization of the monomer, the interface should sustain strain, constitute itself the weakest part throughout the entire thickness of the polymer, and tend to fracture. In accordance with the conventional technique, therefore, even the use of the monomer for promoting adhesion fails to produce sufficient adhesive strength unless an oxide of tributyl borane is used in combination with ferric chloride.
Indeed, the oxide of tributyl borane plus the iron chloride is effective in the polymerization which proceeds inwardly from the dentinal interface. The adhesive agent which uses the oxide of tributyl borane, however, suffers the inevitability of using the oxide of tributyl borane in a proportion of 10% or more based on the amount of the monomer, retarding the curing, limiting the polymerizing monomer virtually to methyl methacrylate alone, and prohibiting use of dimethacrylates.
A photopolymerizing dental material made of a vinyl monomer, camphor quinone, and a 5-alkylbarbituric acid has been known in the art (JP-B- 59-28,569(1994)). Since this material necessitates irradiation with light, it is unfit for adhesion to the interface of a dentin.
We formerly found the fact that 5-n-butyl barbituric acid and cupric chloride are allowed polymerization at interface when they are combined with methyl methacrylate ("Dental Materials and Instruments," Vol. 8, Special Issue No. 14, pp. 89-90 (1989)).
Since 5-n-butyl barbituric acid imparts no sufficient adhesive strength and exhibits poor solubility to the monomers, however, the combination using it has the disadvantage that it must be consumed in a large amount and fails to cure quickly.
An object of this invention, therefore, is to provide a novel polymerization initiator composition controlling polymerization at interface and a curable composition containing it.
Another object of this invention is to solve the problems attendant upon the conventional techniques as described above by devising means of initiating the curing from the interface rich in moisture and consequently provide a polymerization initiator which exhibits outstanding adhesive strength to the dentins of teeth rich in moisture, necessitates only a small consumption, cures quickly, and allows use of a wide variety of monomers as polymerizable monomers besides MMA and also provide a composition containing the polymerization initiator.